The Centre for Offshore Foundations Systems (COFS) at the University of Western Australia has completed several series of tests on suction buckets, said to have shown the potential for further cost savings for the foundation concept.
Conducted at the National Geotechnical Centrifuge Facility in Perth, the tests investigated the response during suction installation demonstrating reliable installation into a variety of seabed soil conditions, including dense sand and clay/sand layered soils, COFS said.
According to the centre, tests of half suction buckets against a transparent window with Particle Image Velocimetry (PIV) analysis of the images taken during installation have revealed new insights into the behavior that cannot be obtained in standard model testing or offshore installations as they do not allow observing the suction bucket inside.
The study also focused on the response under cyclic vertical loading into tension, COFS said, emphasizing that the results confirm considerable increases in tensile capacity due to the relatively short duration of each wave loading event of a storm, which allows the potential for material savings without compromising stability.
“We are able to see inside suction buckets during the installation process, capturing images that reveal the underlying physical processes. Our data showed substantial temporary increases in tensile capacity during storm loading conditions,” said Associate Professor Britta Bienen. “This is currently conservatively ignored in design.”
The researchers used 3.6m and 10m diameter centrifuges that spin the soil sample at approximately 150km/h, with the entire test performed using robotic actuators controlled from a separate command room.
The reduced-scale of the model is balanced by the enhanced gravity field in the centrifuge, such that the stress-sensitive soil response is similar to the full-scale foundation in the field, providing physical evidence of suction bucket response under controlled conditions that relate to the field by established scaling laws, COFS said.